The invention relates to a vane pump with movable vanes and more particularly to a pressure plate on the pump.
Vane pumps of the type addressed here are known. They are used, for example, to provide a fluid for a power steering system in a motor vehicle. They have a pump unit which comprises a cam ring and a rotor which is rotatably mounted in the latter. Said rotor is provided with slots which run radially with respect to the axis of rotation and in which vanes are mounted such that they can move in the radial direction. During the rotation of the rotor in the interior of the cam ring, spaces which become larger and smaller are formed by the vanes, so that at least one each of a suction region and a pressure region are produced. Provided on at least one side of the pump unit is a pressure plate, which forms a lateral boundary surface for the suction and pressure regions. When the pump is operating, the pressure plate is pressed against the pump unit, which sharply increases the wear. In order to counteract this, an appropriate clearance between the cam ring and rotor is provided when the pump is being assembled, as a result of which the volumetric efficiency is often not adequate.
U.S. Pat. No. 3,695,791 discloses a vane pump in which a domed pressure plate produced from a bimetal is used. The pressure plate is installed with such a bias that a predetermined spacing remains between the pressure plate and the rotor and such that the pressure plate is clamped flat between the housing and the rotor. The bimetal function of the sealing washer is intended to maintain this spacing during the operation of the pump. Should the pressure plate be bent under a pressure arising during the operation of the pump, then if the fluid to be delivered heats up, the bending is cancelled out, since the bimetal is correspondingly heated and counteracts the deflection caused by the pressure forces, in that the pressure plate snaps back. It has been shown that, in the case of the known pump, an adequate volumetric efficiency cannot be ensured in every case.